In an optical system employing free-space optical components with pixel-based light modulation, such as reflective spatial light modulators or reflective or transmissive liquid crystal displays, it is important that the light beam be properly aligned with the modulating elements. The light beam also must be properly aligned with the other optical components within the optical system. Mechanical alignment is presently used to position the components in a free-space optical system such that proper alignment is established. Such mechanical alignment can be a time-consuming and laborious process. Typically, the assembler of the system monitors received and/or transmitted power levels in various stages within the system as the positioning of the components is tweaked using mechanical, piezoelectric, or other forces to move components into alignment.
Not only must free-space optical systems and subsystems be initially configured for proper alignment, but such free-space optical systems are prone to instability in their alignment due to, for instance, environmental temperature variation and corresponding Coefficient of Thermal Expansion (“CTE”) mismatches between components made of differing materials within the systems. Thus, over temperature ranges required for operation, e.g., 0-70° C., individual lenses, gratings, mirrors and other components within an enclosure may shift by differing amounts and in different directions. Such shifting may come from the above components, the mounting enclosures and/or adhesives capturing the components having different CTEs.
Other techniques for dealing with environmental stresses and variation include active temperature control and hermetic sealing of components and/or systems. These techniques, however, can be difficult and/or expensive depending upon the size and other system or component design factors.